Method of manufacturing oxide cathodes and cathodes manufactured by such methods



y 1963 H. J. LEMMENS EI'AL 3,088,851

METHOD OF MANUFACTURING OXIDE CATHODES AND CATHODES MANUFACTURED BY suca METHODS Filed Aug. 4. 1960 L /Va Sleeve INVENTOR.

HENDRIC'KUS J1 EMMENJ 026 a] BY M KW AGE I.

United States Patent 3,088,851 METHOD OF MANUFACTURING OXEDE CATH- ODES AND CATHODES MANUFACTURED BY SUCH METHODS Hendrikus Johannes Lemmens, Eindhoven, Jan Bloem, Niimegen, and Edward Fokko de Haan and Marnlus Jacobus Jansen, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 4, 1960, Ser. No. 47,357 Claims priority, application Netherlands Aug. 6, 1959 4 Claims. (Cl. 117-421) This invention relates to methods of manufacturing oxide cathodes wherein a carrier consisting substantially of nickel has provided on it a layer of carbonates of the alkaline-earth metals, to which a powdery metal has been added. The invention also relates to cathodes manufactured by such methods.

lIt is already known to add powdery metal to the layer of carbonates, either in order to improve the electric conductivity in the oxide obtained by thermal decomposition of the carbonates, or as a reducing agent in order to isolate alkaline-earth metal and more particularly barium from the alkaline-earth oxides available.

In conventional cathodes wherein metal has been added to the layer, when used in vacuum tubes, the current density and length of life that can be obtained are hardly better than in cathodes without such addition of metal. In addition, the quality of the cathodes often declines with regard to radiation properties.

An object of the invention is to provide a method yielding improved cathodes.

According to the invention, in a method of manufacturing an oxide cathode in which a carrier consisting substantially of nickel has provided on it a layer of alkalineearth carbonates to which powdery metal is added, the addition to the carbonates consists of manganese in the non-oxidised state. Since it is diflicult to maintain manganese completely free of oxide in working the cathode and in manufacturing the discharge tube, it is advantageous to add the manganese in the form of an alloy which is oxidation-proof, for example MnTi. Cathodes manufactured in this way are found to be capable of delivering for a long time a considerably greater emission current that would be possible without such addition. An explanation of this fact could possibly be found in that during the decomposition of the carbonates, manganese atoms are incorporated into the lattice of the alkalineearth oxide, resulting in the energy levels in the grains being modified so that barium metal is more easily adsorbed at the surface, which adds to the value of the emission current.

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the accompanying drawing in which:

FIG. 1 is a sectional view of one embodiment of a cathode according to the invention; and

FIG. 2 is a sectional view of another embodiment of a cathode according to the invention.

3,088,851 Patented May 7, 1963 "ice As shown in FIG. 1, a cathode tube 1 consisting of nickel and 0.1% of Si and 0.05% of Mg has sprayed onto it a layer 2 of barium-strontium carbonate having a thickness of 40 microns and a size of grain of about 20 microns. The molecular ratio of Ba to Sr is 50:50. The powder 3 of an alloy of manganese and titanium containing of manganese is mixed with the carbonate powder. This material, which is oxidation-proof in air, has a size of grain of about 10 microns. Coarser grains may protrude from the coating. Finer grains might be oxidized.

After incorporation of the cathode in a discharge tube and decomposition of the carbonates, the cathode can continuously deliver a current of l a./cm. for 15 hours at 780 C. cathode temperature. The activation schedule of this cathode which reaches its normal temperature of 780 C. at a heater voltage of 6.3 v. is as follows. While the tube is continuously pumped the heater voltage is kept at 7.5 v. (about 950 C.) until the pressure is below 5 microns of mercury column. Then the heater voltage is kept at 8.4 v. (about 1050" C.) for one minute and at 10 v. (about 1120 C.) for another minute. Thereafter the heater is held at 8 v. until the cathode delivers 4 a./cm. The tube is taken from the pump and the heater held at 7 v. for two hours.

'If oxidation is carefully avoided, it is alternatively possible to use pure manganese powder 4, as shown in FIG. 2, instead of the manganese-titanium alloy. Also instead of BaSr carbonate in a 50:50 ratio, barium-strontium calcium carbonate in a 40:40:20 ratio may be used.

The added amount of powdery metal is not critical and may be varied within comparatively wide limits, for example between 0.5% and 3%. The nickel may also be passive instead of containing reducing agents.

What is claimed is:

1. A method of manufacturing an oxide cathode comprising depositing on a carrier consisting essentially of nickel a layer of alkaline-earth carbonates containing 0.5 to 3% of metallic manganese having an oxide free surface area.

-2. A method as claimed in claim 1, in which the layer of alkaline-earth carbonates contains an alloy of about 70% manganese and the balance titanium.

3. A cathode comprising a nickel base member and a coating thereon of alkaline-earth carbonates containing 0.5 to 3% of metallic manganese having an oxide free surface area.

4. A cathode comprising a nickel base member and a coating thereon of alkaline-earth carbonates containing 0.5 to 3% of an alloy of about 70% manganese and the balance titanium.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MANUFACTURING AN OXIDE CATHODE COMPRISING DEPOSITING ON A CARRIER CONSISTING ESSENTIALLY OF NICKEL A LAYER OF ALKALINE-EARTH CARBONATES CONTAINING 0.5 TO 3% OF METALLIC MANGANESE HAVING AN OXIDE FREE SURFACE AREA. 